Automotive safety critical applications, such as emergency braking to prevent a crash, require that the CMOS imager runs self tests at regular intervals during operation to detect any failure mechanism that may occur due to reliability issues. As other examples, imagers are used as sensors in lane tracking systems, edge-of-road detection systems, near-obstacle-avoidance detection systems, crash alert systems and passenger position sensing systems. Such safety critical applications require imagers with high reliability.
Conventional imagers are tested at the manufacturer using precision equipment to inject a known quantity of light and compare the imager output to the expected output resulting from the known quantity of light. Such test equipment is generally sophisticated and correspondingly expensive. Additionally, operational testing at the manufacturer using precision equipment to inject a known quantity of light and compare the imager output to the expected output resulting from the known quantity of light. Such test equipment is generally sophisticated and correspondingly expensive.
As will be described, the present invention provides systems and methods for testing an image sensor's analog chain, without losing data or frame rate. It may be implemented at a minimal cost and is suitable for both column parallel and serial architecture sensors. The test circuitry may also be used to verify that the sensor's column address range and sequence are correct.
As will also be described, the present invention may provide a test which is inserted into the data path during vertical blanking, such that the test may run without disturbing the regular image capture function of the imager. The test pattern may also be altered for each frame, so that the adequate test coverage is achieved over multiple frames of operation.